This invention relates generally to the field of sensing devices and methods utilizing photo-induced charge movements on a surface or within a membrane or interface to indicate the presence and amount of target chemical substances such as elements, compounds or molecules, both inorganic or organic. More particularly, the invention relates to the field of devices and methods wherein particular dyes or chromophores specific to the target chemical are absorbed onto a surface or membrane and brought into contact with the target chemical analyte, wherein the dyes or chromophores generate electrical signals from charge movements upon exposure to light, and wherein the difference in photo-induced charge movements resulting from the presence of the target chemical relative to the expected photo-induced charge movements in the absence of the target chemical is analyzed to determine the presence of and the quantity of the target chemical present.
There are numerous instances where knowledge of the presence and quantity of a particular substance is required or desirable. Many qualitative and quantitative tests are known in the scientific arts. A number of these tests require either expensive equipment to analyze the test sample, analysis of the sample at a location remote from the sample collection location, or relatively long time periods to produce the result. It is an object of this invention to provide a device and a method which eliminates or reduces these drawbacks, where the detection and quantification of a target substance can be rapidly, accurately and relatively inexpensively achieved.
As an example of a target substance of negative effect in the real world, the invention can be explained using guanine as a representative target substance, guanine being the most prevalent nitrogenous waste produced by dust mites feeding on nitrogen-rich substances. It is estimated that about 5 percent of the population suffer from asthmatic or allergic symptoms attributable to house dust, with the most significant type of household allergens being contained in the feces of dust mites and in fragments of dead mite bodies, resulting from digestive enzymes excreted by the mites. Dust mite allergens are very resistive proteins, such that many common oxidizing or reducing agents, divalent and trivalent cations, alkalis, aldehydes, mild acids and some proteolytic enzymes have no effect in reducing the allergenicity of house dust mite allergens. Mite fecal pellets remain allergenic for many years, even when active mite colonies have been exterminated. Dust mite fecal pellets range from 10 to 40 microns in diameter and are easily picked up and transported by air currents. Walking, sitting, fluffing a pillow, changing bedspreads or sheets, etc. distribute the pellets into the air where they are inhaled.
Known methods for detecting the presence of dust mites through guanine include the Bischoff and Schirmacher rapid strip method, which is a qualitative method where the user compares colors of a test strip to a 4-level color chart. This method uses perishable and toxic consumables. Laboratory methods for detecting guanine quantities include High Performance Liquid Chromatography and Capillary Zone Electrophoresis, which are time consuming and relatively expensive. Other methods are used to detect specifically identified mite allergens, but currently only four such allergens are sufficiently characterized, and these four allergens belong to only two species of mites. Still other methods are used to detect the presence of the mites themselves, such as visual counts using a microscope, but the mites must be segregated from the dust samples using flotation or the like, and such processes are time consuming and relatively inaccurate. Such tests further fail to provide information on the presence or quantity of allergens, which as stated can be present in large amounts even where active colonies are not found.
Guanine is also one of the most reactive bases found in DNA and as such may prove to be a sensitive sentinel for DNA-damaging chemicals. For example, propylene oxide is a powerful DNA and guanine methylating agent which is thought to be carcinogenic, and it is estimated by OSHA that over half a million American workers are exposed to this chemical each year through direct contact with feedstock and disinfectants or by contact with residues on food surfaces.
As an example of other target substances, the invention can be used to quantify particular strains of bacteria or other microorganisms, such as for example as a means to determine if water is sufficiently sanitized for drinking purposes. Bioreactors used to produce a wide range of products from brewers yeast to human insulin can be monitored. DNA, RNA, sugars and primary amines are other target substances which may be detected.
The invention may also be used to detect and quantify metals including but not limited to Ac, Al, Ag, Am, Au, B, Ca, Cm, Co, Cr, Cu, Fe, Fl, Hf, I, In, K, Mg, Mn, Mo, Ni, Pa, Pb, Po, Pt, S, Th, Ti, U, Zn and Zr. Other target substances include but are not limited to dissolved gases, acid and alkaline phosphatases, dioxin, indole, nitrates, polysaccharides, sialomucins, skatole, sulfates, sulfomucins, trytophan, tyrosine, and uranic acid mucins.